So I called
DCL because I have a placeholder that will be expiring on March 1st, 2021. Evidently if you use it before the expiration date and reserve a cruise after that expiration date (I picked a Magic cruise April 17th 2021) it still gives you the discount. She tried it for me and it worked. Not sure why but she seemed to know about it because she suggested doing it. She also said she was excited to go to the cast member preview reopening of Magic Kingdom tomorrow.